Vacuum chucks have been heretofore generally used as holding apparatuses for holding workpieces. The vacuum chucks have a problem that thin plates chucked by the vacuum chucks deform around the chucked parts. By contrast, electrostatic holding apparatuses such as electrostatic chucks do not cause thin plates to deform around the chucked parts even when handling (holding) the thin plates, because the electrostatic chucks are designed to be capable of holding workpieces by use of an electrostatic force of the entire electrode surfaces (see Patent Documents 1 and 2, for example).
For example, an electrostatic chuck shown in FIGS. 6 and 7 is known as the electrostatic holding apparatus of this kind. As shown in FIG. 6, this electrostatic chuck includes a base board 201 and a holding section 110 attached to the base board. The holding section 110 is formed of: an electrode configured of an electrode element group 202a and an electrode element group 202b; and an insulating layer 203 covering this electrode. The base board 201 is fixed to the back surface 203b of this insulating layer 203. In addition, these electrode element groups 202a and 202b are electrically connected to a DC (direct current) high-voltage power supply 122 via switches 121a and 121b, respectively.
As shown in FIG. 7, the holding section 110 shown in FIG. 6 includes a capacitor 112 for accumulating electric charges and a resistor 111.
In the case of the electrostatic holding apparatus of this type, an ON operation of the switches 121a and 121b causes a high voltage of +V volts to be applied to the electrode element group 202a, and a high voltage of −V volts to be applied to the electrode element group 202b, respectively. Thereby, when the switches 121a and 121b are ON, a front surface 203a of the insulating layer 203 turns into a holding surface, and thus an electrostatic attraction is induced between the holding surface 203a and a handled workpiece 205. Thus, the handled workpiece 205 is attracted to, and held on, the holding surface 203a by the electrostatic attraction.
During this attraction, in the capacitor 112 of the holding section 110, an electric potential causing the electrostatic attraction is maintained, whereas a steady-state leakage current occurs in the resistor 111 (the insulating layer 203 between the electrode element group 202a and the electrode element group 202b). The volume resistivity of the resistor 111 (the insulating layer 203) is usually 1014 μm or more. In a case where an electrode with a surface dimension of 200 mm×200 mm is used, the amount of this steady-state leakage current is as small as approximately 1 nA or less.
When the switches 121a and 121b are OFF, the voltage of the DC high-voltage power supply 122 is cut off. The leakage current between the electrode element group 202a and the electrode element group 202b continues occurring. Although this leakage current flows in a trace amount such as approximately 1 nA, the leakage current gradually decreases the electric potentials respectively of the electrode element group 202a and the electrode element group 202b, and thus reduces the electrostatic attraction. In the holding section 110 as shown in the schematic circuit diagram, during this reduction, the electric potential of the capacitor component 112 is reduced due to consumption of electric charges gradually leaking through the high-resistance component 111.
Thereby, when the switches 121a and 121b are OFF, the electrostatic attraction of the holding section 110 decreases, and thus the force for holding the handled workpiece 205 decreases. Eventually, the handled workpiece 205 is released from the holding surface. In a case where the handled workpiece 205 is intended to be released quickly, an illustrated grounding operation is performed.
In the case of the electrostatic chuck of this type, the ON operation of the switches 121a and 121b causes the constant high-voltages (for example, +V volts to the electrode element group 202a, and −V volts to the electrode element group 202b) to be outputted whereas the OFF operation of the switches 121a and 121b cuts off these voltages. Thereby, when the switches 121a and 121b are ON, the front surface 203a of the insulating layer 203 turns into the holding surface, and thus the electrostatic attraction is induced between the holding surface 203a and the handled workpiece 205. As a result, the handled workpiece 205 is attracted to, and held on, the holding surface 203a by the electrostatic attraction. When the switches 121a and 121b are OFF, the electrostatic attraction is dissolved, and the handled workpiece 205 is released from the holding surface 203. In this manner, the electrostatic chuck of this type is capable of attracting and holding (loading) a handled workpiece such as a conductor, a semiconductor and a high-resistance resistor by the electrostatic attraction, and of detaching (unloading) the handled workpiece when releasing the handled workpiece.    Patent Document 1: JP-A 2004-335811 (FIG. 11)    Patent Document 2: JP-A 2003-282671 (FIGS. 1 and 2)